1. Field of the Invention
The present invention relates to an organic electroluminescence (organic EL) element and a manufacturing method therefor.
2. Description of the Related Art
An electroluminescence element (EL element) is a solid element which has high impact resistance and emits lights with high visibility. The use of an EL element as a light emitting element has been attempted in various display devices. Especially, organic EL elements have been recently developed which have structures such as the following:
cathode/light emission layer/hole injection layer/anode;
cathode/electron injection layer/light emission layer/anode;
cathode/electron injection layer/light emission layer/hole injection layer/anode; or
anode/light emission layer/electron injection layer/cathode. The organic EL elements show various superior properties, such as the capability to emit light with high brightness and high efficiency by merely applying a voltage between the cathode and the anode, and the capability to show multicolor.
As shown in FIG. 5, an example of the organic EL element is formed by laminating, on a glass substrate 1, transparent electrodes 2 as anodes, an organic EL layer consisting of a hole injection layer 3, a hole transport layer 4, light emission layers 5, an electron transport layer 6, and a cathode 7, in the above order.
The transparent electrodes (anodes) 2 are generally made of indium tin oxide (ITO). The cathode 7 is made of an alloy or a mixture of magnesium and a group II metal.
The light emission layers 5 are provided between the anodes 2 and the cathode 7. The light emission layers 5 are formed respectively into patternings of a red light emission layer 5a, a green light emission layer 5b, and a blue light emission layer 5c. Moreover, the hole injection layer 3, the hole transport layer 4, and the electron transport layer 6 are provided in that order between the anodes 2 and the cathode 7, so that the organic EL element can emit light with high brightness and high efficiency.
When a voltage is applied between the anodes 2 and the cathode 7, the light emission layers 5 of the organic EL element emit light. Each layer of the organic EL element has a thickness of 200 nm or less, except for the insulating organic layers 18 and the cathode 7.
In the organic EL element shown in FIG. 5, the anodes 2 are formed into a patterning over a glass substrate 1 by using a photolithography technique, followed by forming films of a hole injection layer 3, a hole transport layer 4, light emission layers 5, an electron transport layer 6, and a cathode 7, in that order.
However, when the anodes 2 are made of ITO, the workability of the patterning becomes low. For example, when the wet etching technique is used to improve productivity, both pattern edges 2a, 2a of the anode 2 made of ITO become rough and form taper angles of 15 to 90xc2x0, on which the hole injection layer 3, the hole transport layer 4, and the electron transport layer 6 are then respectively formed into films, in that order. Therefore, the thicknesses of the hole injection layer 3, the hole transport layer 4, and the electron transport layer 6 become irregular, generating thin or convex portions on which local film damage is caused by an applied voltage, and a short circuit is caused by a concentration of an electrical field. Thereby, the cathode 7, which was last to be formed into a film, is in danger of being cut, resulting in a decrease in the reliability of the organic EL element.
In order to prevent the generation of a short circuit and the breaking of the cathode 7, a method, in which an insulating material is provided between opposite electrodes, is disclosed in Japanese Patent No. 2734464.
However, in the method of providing the insulating material between the opposite electrodes, in addition to an evaporation apparatus, other filmforming apparatuses, patternforming apparatuses, and the like, are required, so that the number of processes and the required cost for manufacturing the organic EL element increase.
When polyimide is used as the insulating material and is formed into a film between the opposite electrodes using spin coating techniques, for example, dark spots, which darken the light emission areas, are increased due to a small quantity of moisture included in the polyimide film.
The present invention has been made to solve the problems described above. An object of the present invention is to provide an organic EL element which can be produced at low cost and which can improve the reliability by preventing problems such as the generation of a short circuit and the breaking of a cathode thereof, and to provide a manufacturing method therefor.
The present invention provides an organic EL element including a plurality of transparent electrodes arranged in parallel on a base plate; a plurality of cathodes disposed above organic layers so as to cross the transparent electrodes; said organic layers including light emission layers and disposed between the transparent electrodes and the cathodes; and an insulating organic layer disposed in spaces between adjacent transparent electrodes. The insulating organic layers may comprise overhanging portions to cover the lateral end portions of the transparent electrodes. The overhanging portion may have a taper angle at each lateral end thereof, and the thickness of the overhanging portion decreases from the inside to the outside of the insulating organic layers in the width direction of the insulating organic layer. The taper angle of the overhanging portion may be set within the range of 0.01 to 70xc2x0.
The maximum film thickness of the insulating organic layer may be set within the range of 10 to 500 nm. The widths of the overhanging portions may be set within the range of 1 to 15 xcexcm. The insulating organic layer is made of at least one material used for the organic layer.
Moreover, the present invention provides a manufacturing method of an organic EL element comprising a plurality of transparent electrodes arranged in parallel on a base plate; a plurality of cathodes disposed above organic layers so as to cross the transparent electrodes; said organic layers including light emission layers and disposed between the transparent electrodes and the cathodes; and an insulating organic layer disposed in spaces between adjacent transparent electrodes, the method comprising the steps of: forming the insulating organic layer; forming the organic layer; and forming of the cathode, wherein the steps of forming the insulating organic layer, the organic layer, and the cathode are carried out in a vacuum state.
Since the organic EL element of the present invention has the insulating organic layer disposed in the spaces between the adjacent transparent electrodes, a taper angle generated in the vicinity of a lateral end portion of the transparent electrode can be prevented from becoming steep, so that the organic layer and the cathode can be formed smoothly. Therefore, the cathode is prevented from breaking, and the film thickness of the organic layer is prevented from becoming thin and is uniformly formed, so that the generation of a short circuit can be also prevented.
When the insulating organic layers comprise overhanging portions to cover the lateral end portions of the transparent electrodes, even if the lateral end portions of the transparent electrodes are rough, the taper angle generated in the vicinity of the lateral end portion of the transparent electrodes can be prevented from becoming steep. Therefore, the variation of the film thickness of the organic layer, local film damage caused by an applied voltage, a short circuit caused by a concentration of an electric field, and the breaking of the cathode can be prevented.
When the overhanging portion has a taper angle at each lateral end thereof, and the thickness of the overhanging portion decreases from the inside to the outside of the insulating organic layers in the width direction of the insulating organic layer, the taper angle in the vicinity of the lateral end portions of the transparent electrodes can be prevented from becoming steep, so that the organic layer and the cathode can be formed smoothly. When the taper angle of the overhanging portion is set within the range of 0.01 to 70xc2x0, the problems described above can be prevented more effectively.
When the maximum film thickness of the insulating organic layer is set within the range of 10 to 500 nm, the cathode can be formed smoothly, so that the cathode is prevented from breaking, and the film thickness of the organic layer is prevented from becoming exceedingly thin and is uniformly formed, so that the generation of a short circuit can be also prevented.
When the insulating organic layer is made of at least one material used for the organic layer, the steps of forming the insulating organic layer, the organic layer, and the cathode, can be carried out in a vacuum state, so that the total number of manufacturing steps and the manufacturing cost can be reduced.
In the manufacturing method of the organic EL element, by forming the insulating organic layer which may be made of at least one material used for the organic layer, the generation of dark spots, which are caused by moisture generated by patterning polyimide and the like and which darken the light emission areas, can be prevented. Moreover, since all of the steps can be carried out in a vacuum state, the number of manufacturing steps and the cost for manufacturing can be reduced, in comparison with the photolithography method using polyimide.